Adaptive Loop Filtering (ALF) for Video Coding

Abstract

A method for adaptive loop filtering of a reconstructed picture in a video encoder is provided that includes determining whether or not sample adaptive offset (SAO) filtering is applied to the reconstructed picture, and using adaptive loop filtering with no offset for the reconstructed picture when the SAO filtering is determined to be applied to the reconstructed picture.

1 . A system comprising:
 a decoder configured to:
 determine, from a bit stream, that sample adaptive offset (SAO) filtering is to be applied to a first image; 
 apply adaptive loop filtering (ALF) to the first image without decoding a first ALF offset in the bit stream for the first image; 
 determine that SAO filtering is to not be applied to a second image; 
 decode a second ALF offset for the second image; and 
 apply ALF to the second image using the second ALF offset; and 
   a display coupled to the decoder and configured to display the first image and display the second image.   
     
     
         2 . The system of  claim 1 , wherein the decoder is configured to:
 decode a first set of coefficients for the first image;   apply ALF to the first image using the first set of coefficients;   decode a second set of coefficients for the second image; and   apply ALF to the second image using the second ALF offset and the second set of coefficients.   
     
     
         3 . The system of  claim 1 , wherein to apply ALF to the first and second images, the decoder is configured to apply finite impulse response filters to the first and second images. 
     
     
         4 . The system of  claim 3 , wherein to apply the finite impulse response filters to the first and second images, the decoder is configured to apply symmetric two-dimensional finite impulse response filters to the first and second images. 
     
     
         5 . The system of  claim 1 , wherein the display includes a light emitting diode display configured to display the first image and display the second image. 
     
     
         6 . The system of  claim 1 , wherein the display includes a liquid crystal display configured to display the first image and display the second image. 
     
     
         7 . A system comprising:
 a receiver configured to receive a bit stream; and   a decoder coupled to the receiver and configured to:
 determine, from the bit stream, that sample adaptive offset (SAO) filtering is to be applied to a first image; 
 apply adaptive loop filtering (ALF) to the first image without decoding a first ALF offset in the bit stream for the first image; 
 determine that SAO filtering is to not be applied to a second image; 
 decode a second ALF offset for the second image; and 
 apply ALF to the second image using the second ALF offset. 
   
     
     
         8 . The system of  claim 7 , wherein the decoder is configured to:
 decode a first set of coefficients for the first image;   apply ALF to the first image using the first set of coefficients;   decode a second set of coefficients for the second image; and   apply ALF to the second image using the second ALF offset and the second set of coefficients.   
     
     
         9 . The system of  claim 7 , wherein to apply ALF to the first and second images, the decoder is configured to apply finite impulse response filters to the first and second images. 
     
     
         10 . The system of  claim 9 , wherein to apply the finite impulse response filters to the first and second images, the decoder is configured to apply symmetric two-dimensional finite impulse response filters to the first and second images. 
     
     
         11 . The system of  claim 7 , further comprising a light emitting diode display coupled to the decoder and configured to display the first image and display the second image. 
     
     
         12 . The system of  claim 7 , further comprising a liquid crystal display coupled to the decoder and configured to display the first image and display the second image. 
     
     
         13 . A method comprising:
 determining, from a bit stream, that sample adaptive offset (SAO) filtering is to be applied to a first image;   applying adaptive loop filtering (ALF) to the first image without decoding a first ALF offset in the bit stream for the first image;   determining that SAO filtering is to not be applied to a second image;   decoding a second ALF offset for the second image;   applying ALF to the second image using the second ALF offset; and   displaying the first image and display the second image.   
     
     
         14 . The method of  claim 13 , further comprising:
 decoding a first set of coefficients for the first image, wherein applying ALF to the first image uses the first set of coefficients; and   decoding a second set of coefficients for the second image, wherein applying ALF to the second image uses the second ALF offset and the second set of coefficients.   
     
     
         15 . The method of  claim 13 , wherein applying ALF to the first and second images comprises applying finite impulse response filters to the first and second images. 
     
     
         16 . The method of  claim 15 , wherein applying the finite impulse response filters to the first and second images comprises applying symmetric two-dimensional finite impulse response filters to the first and second images. 
     
     
         17 . The method of  claim 13 , wherein displaying the first and second images is via a light emitting diode display. 
     
     
         18 . The method of  claim 13 , wherein displaying the first and second images is via a liquid crystal display. 
     
     
         19 . A system comprising:
 a decoder configured to:
 decode a flag from a bit stream, wherein the flag indicates whether adaptive loop filtering (ALF) with an offset is used; 
 decode a parameter set for a picture from the bit stream; 
 apply ALF to at least a first portion of the picture using the parameter set without using the offset in response to determining that the flag indicates ALF without the offset is used; and 
 apply ALF to at least a second portion of the picture using the offset signaled in the parameter set in response to determining that the flag indicates ALF with the offset is used; and 
   a display configured to display the picture.   
     
     
         20 . The system of  claim 19 , wherein the decoder is configured to apply ALF apply ALF to at least the first portion of the picture without addition of the offset.